The present invention is directed to a method for transmitting a digital broadband signal having the bit rate of an intermediate hierarchy level via a multiplexing device, via a link in a network having network node equipment controlled by an exchange and via a demultiplexing device of a synchronous digital multiplex hierarchy.
Bit rates of 1544 kbit/s, 6312 kbit/s and 44736 kbit/s are used in the North American hierarchy. The European hierarchy operates with, among others, bit rates of 2048 kbit/s; 8448 kbit/s and 34368 kbit/s. Intermediate hierarchy levels can be formed by a multiple of these bit rates.
The synchronous digital multiplex hierarchy (SDH) is defined in CCITT recommendations G.707, G.708 and G.709. According to the last-cited recommendation, the transmission of tributary unit concatenations is also provided. In the TM3 Meeting (Transmission and Multiplexing) in Brussels from Apr. 24-28, 1989 of the European Transmission Standards Institute ETSI, a multiplexing structure was proposed and the formation of tributary unit concatenations was proposed in Temporary Documents No. 42, 62 and 110 in Aveiro Oct. 23-28, 1989.
FIG. 1 depicts the multiplexing structure that was revealed at the TM3 Meeting. Reference characters are defined as follows: A denotes section, AU denotes administration unit, C denotes container, H denotes digital signal, POH denotes path overhead, PTR denotes pointer, SOH denotes section overhead, STM denotes synchronous transport module, TU denotes tributary unit, TUG denotes tributary unit group and VC denotes virtual container.
Instead of the numbers following C, TU, TUG and VC, an n is placed in that position for a general case. The number of parallel lines provided is indicated at the lines.
FIG. 2 depicts a network N for the synchronous digital multiplex hierarchy SDH having the network node equipment (cross-connect) CC and having an exchange (telecommunication management network) TMN that controls them. The link provided between a multiplexing equipment MUX and a demultiplexing equipment DEMUX and provided with cross-connects CC1 through CC5 is emphasized by a thick line. Only one transmission direction is thereby shown.
The broadband signals DS to be transmitted are inserted into containers C-n in the multiplexing equipment M on the basis of positive filling. Each of these containers is supplemented by the addition of a path overhead VC-n POH to form a virtual container VC-n that is periodically transmitted in a synchronous transport module STM-1. The first byte of a virtual container VC-n is indicated by a pointer AU-n PTR or TU-n PTR whose value defines the initial position of the virtual container in the transmission frame. As such, the virtual container VC-n usually serves a higher hierarchy level. Together with the pointer AU-n PTR or TU-n PTR allocated to it, such a virtual container forms a tributary unit AU-n or TU-n. A plurality of these having the same structure can in turn be combined to form a tributary unit group TUG-n. There are tributary unit groups TUG-21 and TUG-32 for the North American 1.5-Mbit/s hierarchy and TUG-22 and TUG-31 for the 2-Mbit/s hierarchy that, among others, is standard in Europe.
According to the afore-mentioned CCITT recommendation G.709, Section 3.3.7, tributary units TU-21 having a bit rate of 6312 kbit/s or TU-22 having a bit rate of 8448 kbit/s can be concatenated. In the Temporary Documents that have likewise been cited, a concatenation of tributary units TU-11 having a bit rate of 1544 kbit/s or TU-12 having a bit rate of 2048 kbit/s is also proposed. For example, a 11200-kbit/s signal can be transmitted for future services as a tributary unit concatenation TU-12-5c (5.times.VC-12=5.times.2240 kbit/s, maximum bit rate) for a LAN (local area network) coupling or other broadband signals. The position character c indicates the concatenation.
FIG. 3 depicts a section AB' expanded in comparison to the section AB of the multiplexing structure of FIG. 1 bounded by a broken line. This can basically contain additional containers C-12-mc, C-22-mc and C-31-mc, virtual containers VC-12-mc, VC-22-mc and VC-31-mc and tributary units TU-12-mc, TU-22-mc and TU-31-mc.
For example, a broadband signal having a bit rate of 11200 kbit/s can be supplied via the input E1 when m=5 is selected. A tributary unit concatenation TU-12-5c is formed via a container C-12-5c and a virtual container VC-12-5c. A broadband signal of m.times.8448 kbit/s can also be supplied via the input E2 and a broadband signal of m.times.34368 kbit/s can be supplied via the input E3. Further inputs are conceivable. A different number can be respectively set for m.
Such an arrangement can be correspondingly inserted into the upper half of the multiplexing structure of FIG. 1.
In tributary unit concatenations, a pointer is allocated to the first tributary unit, this indicating the beginning thereof in a virtual container given the incorporation of the tributary unit concatenation in a virtual container. Instead of a pointer, all further tributary units contain a concatenation indicator CI. This indicates that the tributary unit concatenation must be kept together and that the pointer operations of the preceding tributary unit must be implemented in the same manner for the following tributary unit. As FIG. 4 depicts, identical pointer skips PS must be undertaken in the other tributary units TU-12.sub.2 through TU-12.sub.5 given a pointer skip PS for clock matching of the first tributary unit TU-12.sub.1 with the 11200-kbit/s signal. What is thereby achieved is that the sequence of the bytes is not disturbed.
For example, a pointer skip can occur in a cross-connect CC when the tributary unit concatenation TU-12-5c contained in a standard transport module STM-1 is refilled into a different standard transport module STM-1.
In this method, every cross-connect must comprise means (hardware and software) for processing these concatenation indicators and for the common pointer skip of the tributary unit concatenation. This requires a special control. What is also compulsory is that the tributary units of a tributary unit concatenation are also successively transmitted.
It was also proposed to directly concatenate successive tributary units in a virtual container (German reference P 4018687.3). This, however, has the disadvantage that a mixing of a tributary unit concatenation having m=4 with tributary units TU-31 is not possible in the same standard transport module STM-1. Four concatenated tributary units TU-12 already respectively occupy a column in the frame of the four tributary unit groups TUG-37. Since a closed 34-Mbit/s signal requires the space of a tributary unit group TUG-31, it cannot be transmitted in the same standard transport module STM-1.